1. Field of Invention
The current invention relates to lithographically produced structures, and more particularly to reconfigurable lithographically produced structures.
2. Discussion of Related Art
Lithography, the workhorse of the microelectronics industry, is routinely used to fabricate micro and nanostructures in a highly monodisperse manner, with high accuracy and precision. However, one of the central limitations of this technology is that it is inherently two-dimensional (2D) as a result of the wafer based fabrication paradigm. It is extremely challenging to fabricate three-dimensional (3D) patterned structures, let alone complex structures containing encapsulated objects, on the sub-mm scale. Thus, the parallel fabrication of such structures remains a major challenge that needs to be addressed.
Some solutions have emerged that enable sub-mm scale lithographic fabrication in 3D; these include techniques such as wafer stacking (N. Miki, X. Zhang, R. Khanna, A. A. Ayon, D. Ward, S. M. Spearing, Sens. Actuators, A 2003, 103, 194-201), micromachining (S. Kawata, H. B. Sun, T. Tanaka, K. Takada, Nature 2001, 412, 697-698), molding (L. T. Romankiw, Electrochim. Acta 1997, 42, 2985-3005; L. Weber, W. Ehrfeld, H. Freimuth, M. Lacher, H. Lehr, B. Pech, presented at Micromachining and Microfabrication Process Technology II, Austin, Tex., USA, October 1996), and self-assembly (G. M. Whitesides, B. Grzybowski, Science 2002, 295, 2418-2421). Self-assembly, or self-folding, of 2D lithographically patterned templates is one attractive strategy for fabricating 3D patterned, sub-mm scale structures. There are numerous methods that enable self-folding, such as surface tension-based assembly (R. R. A, Syms, E. Yeatman, V. M. Bright, G. M. Whitesides, J. Microelectromech. Syst. 2003, 12, 387-417; T. G. Leong, P. A. Lester, T. L. Koh, E. K. Call, D. H. Gracias, Langmuir 2007, 23, 8747-8751), electroactive polymer actuation (E. W. H. Jager, E. Smela, O. Inganas, Science 2000, 290, 1540-1545), electric actuation (K. Suzuki, I. Shimoyama, H. Miura, J. Microelectromech. Syst. 1994, 3, 4-9; K. Suzuki, H. Yamada, H. Miura, H, Takanobu, Microsyst. Technol. 2007, 13, 1047-1053), thermal and shape memory alloy actuation (J. K. Luo, J, H, He, Y. Q. Fu, A, J. Hewitt, S. M. Spearing, N. A. Fleck, W. I. Milne, J. Micromech. Microeng. 2005, 15, 1406-1413; J. K. Luo, R. Huang, J. H. He, Y. Q. Fu, A. J. Flewitt, S. M. Spearing, N. A. Fleck, W. I. Milne, Sens. Actuators, A 2006, 132, 346-353; A. P. Lee, D. R. Ciarlo, P. A. Krulevitch, S. Lehew, J. Trevino, M. A. Northrup, Sens. Actuators, A 1996, 54, 755-759), and stress-driven actuation (W. J. Arora, A. J. Nichol, H. I. Smith, G. Barbastathis, Appl. Phys. Lett. 2006, 88, 053108; C. L. Chua, D. K. Fork, K. Van Schuylenbergh, J.-P. Lu, J. Microelectromech. Syst. 2003, 12, 989-995; E. Moiseeva, Y. M. Senousy, S. McNamara, C. K. Harnett, J. Micromech. Microeng. 2007, 17, N63-N68; O. G. Schmidt, K. Eberl, Nature 2001, 410, 168). However, most previous demonstrations of lithographically patterned, self-folding microstructures are assembled tethered to substrates. Additional limitations include high temperature assembly incompatible with aqueous media or spontaneous assembly once the underlying support layer is dissolved. Thus, versatile on-demand encapsulation of objects within self-assembled structures remains even more of a challenge and has not been previously demonstrated.
Our research group has demonstrated a process that utilized an electrodeposited solder as a hinge for the self-assembly of lithographically structured microcontainers (T. G. Leong, P. A. Lester, T. L. Koh, E. K. Call, D. H. Gracias, Langmuir 2007, 23, 8747-8751). However, the assembly could only be carried out at high temperature (188° C.), in the presence of soldering flux, and in high boiling point (non-aqueous) media. These microcontainers could only be loaded after assembly. Lower temperature assembly has been demonstrated in aqueous media using a low melting point solder (mp 47° C.) (M, Boncheva, G. M. Whitesides, Adv. Mater. 2005, 17, 553-557); however, the structures fabricated were on the millimeter to centimeter scale, and the templates were fabricated by hand in a serial manner. Also, since the low melting point solder used is a stoichiometrically complex bismuth alloy that is deposited by dip-coating; low temperature, parallel, wafer scale self-folding of smaller microstructures has remained a challenge.
Therefore, there remains a need for improved reconfigurable, lithographically produced structures.